1. Field of the Invention
The present invention relates to a method and an apparatus to control a disc drive, and more particularly, to a method and an apparatus to write and inspect servo information in a disc drive, that minimizes an effect of servo information written in adjacent tracks caused by a gap erase field in a disc drive, and also performs servo information inspection and defect processing.
2. Description of the Related Art
A hard disc drive includes a plurality of magnetic transducers that sense a magnetic field and magnetize a single rotating disc, or each of a plurality of rotating discs, to write and read information, on and from the disc. In general, such information is formatted in a plurality of sectors in circular tracks. There is a number of tracks across each surface of a disc. Corresponding tracks on adjacent discs of the plurality of rotating discs are grouped into cylinders. Therefore, each track is also defined by a cylinder.
In general, each of the transducers is integrated into a slider incorporated into a head gimbal assembly (HGA). Each HGA is attached to an actuator arm. The actuator arm has a voice coil adjacent to a magnetic assembly, together with a voice coil motor. In general, the hard disc drive includes a driving circuit, which supplies current used to excite the voice coil motor, and a controller. The excited voice coil motor rotates the actuator arm and moves each of the transducers across the surfaces of disc(s).
When information is written or read, sometimes the hard disc drive performs a seek routine, where each of the transducers is moved from one track to another track. During the seek routine, the voice coil motor is excited by a current to move each of the transducers to a new position on the surface of a disc. Also, the controller executes a servo routine, in which each of the transducers is moved to a position of a track at a center of the track.
Each of the transducers includes a writer to write data and a reader to read data. In a write mode, as shown in FIGS. 1A and 1B, current flows through a pole 1 and a pole 2 of the writer, such that a magnetic field is created to magnetize the disc.
When the magnetic field is created between the pole 1 and the pole 2, as shown in FIGS. 1A and 1B, an undesired gap erase field is also created. As a number of tracks-per-inch (TPI) increases in a high-density writing apparatus, the gap erase field increasingly affects adjacent tracks.
In a general servo track write operation, tracks are written sequentially from 0, the number of a track in an outer portion (OP) of the disc, to the last track in an inner portion (IP). However, as a head (transducer) is placed in the OP, middle portion (MP), or IP, a central axis of the poles 1 and 2 and a track generate positive skew, zero skew, and negative skew, respectively, with respect to a tangent to the track. As shown in FIG. 1B, when servo information is written in an N-th track, moving from the OP toward the track where the skew is ‘0’, the central axis of the poles 1 and 2 generate a positive skew with respect to the N-th track tangent. The gap erase field generated by the positive skew affects an (N+1)-th track. But the servo information is not yet written in the (N+1)-th track, and the servo information will be written in the (N+1)-th track after being written in the N-th track. Thus, from the OP to the track where the skew equals ‘0’, or skew ‘0’, the gap erase field does not affect the servo information in an adjacent field.
But as shown in FIG. 1A, when the central axis of the poles 1 and 2 makes a negative skew with respect to the track tangent, and the magnetic field writes the servo information on the N-th track, the effect of the gap erase field reduces the width of a signal already written in the (N−1)-th field. Thus, the magnitude of a servo signal is reduced in the tracks written after the skew between the axis of the poles 1 and 2 and the track tangent becomes negative. With a reduced magnitude of the servo signal, there is an increased likelihood that the servo signal will be converted into a wrong track value or position error signal (PES) value during an A/D (analog/digital) conversion operation, yielding a result that a normal servo control (seek or following) operation cannot be performed.
To solve these problems, Japanese Patent Publication No. 2001-189062 titled “Disc Memory Apparatus and Servo Data Writing Method”, discloses a technique to reduce an effect of an erase width, in which servo information is written in a radial direction from either an inner portion or an outer portion of a disc, and the servo information is written in the radial direction from the of the inner portion and the outer portion.
However, as shown in FIG. 6, due to limited precision of a servo track writer, servo data are superimposed on a track of an intermediate region, in which a direction of writing servo data is reversed, and the servo data are abnormally written in the superimposed writing region. Also, servo data inspection and track defect processing should be performed in a region in which the servo data are superimposed. However, this technique has not yet been developed, and thus, there is a limitation in applying the technique disclosed in Japanese Patent Publication No. 2001-189062 to a product.